A fiberglass plastic rod must be joined to a metal fitting so as to ensure a high strength of the unit.
There is known a method for joining a fiberglass plastic rod to a metal fitting of an electrical device, whereby one of the ends of the fiberglass plastic rod is sawed along the rod's axis into two parts which are then wedged apart in the cone-shaped cavity of the metal fitting.
This method is disadvantageous in that the wedging affects the mechanical characteristics of the rod. Another disadvantage of this method lies in a concentration of mechanical stresses at the place where the fiberglass plastic rod comes out of the metal fitting.
There is further known a method for joining a fiberglass plastic rod to a metal fitting of an electrical device (cf. Elettrificazione, No. 6, 1971), according to which a hole of a diameter somewhat in excess of that of the fiberglass plastic rod is provided in the metal fitting to receive one of the ends of the fiberglass plastic rod. The whole unit is then pressed on a hydraulic press.
The joining must be done so as to provide a uniform compression, ensure a desired distribution of pressure over the length of the built-in portion of the rod, and keep the rod intact under pressure. To achieve these goals, one must use dies of complex shapes and impose stringent accuracy to size requirements on the metal fittings and fiberglass plastic rods.